A fixing structure for an exhaust gas sensor of an internal combustion engine is known in which an exhaust gas sensor in the form of a heater-less oxygen sensor is installed in an exhaust port in the cylinder head of the engine, with a sensing tip of the sensor positioned in the exhaust port, as disclosed in Patent Document 1, for example.
The structure disclosed in Patent Document 1 includes an engine cylinder head in which a single exhaust port and a single exhaust valve for the exhaust port are provided. To attain an improved output performance of the engine, an engine cylinder head is known in which the exhaust port system includes two upstream exhaust port sections opened and closed by two exhaust valves, respectively, and a single downstream collective exhaust port section into which the two exhaust port sections merge.
In case the exhaust gas sensor is installed in such a cylinder head, the exhaust gas sensor is naturally installed such that the sensing tip of the sensor is located in the collective exhaust port section. In such a case, it is possible that exhaust gas currents from the two upstream exhaust port sections flow onto the exhaust gas sensor in the downstream collective exhaust port section without being sufficiently intermixed. If so, it is possible that the sensing accuracy of the exhaust gas sensor is poor.
For this reason, how the exhaust gas sensor is installed and fixed influences on attaining a good sensing accuracy.